Absolute Neutron Flux Measurements of a D-T Neutron Generator

Nuclear Fusion, 2017

A new DT campaign (DTE2) is planned at JET in 2020 to minimize the risks of ITER operations. In view of DT operations, a calibration of the JET neutron monitors at 14 MeV neutron energy has been performed using a well calibrated 14-MeV neutron generator (NG) deployed, together with its power supply and control unit, inside the vacuum vessel by the JET remote handling system. The neutron generator was equipped with two calibrated diamond detectors, which continuously monitored its neutron emission rate during the calibration, and activation foils which provided the time integrated yield. Cables embedded in the remote handling boom were used to power the neutron generator, the active detectors and pre-amplifier, and to transport the detectors' signal. The monitoring activation foils were retrieved at the end of each day for decay -ray counting, and replaced by fresh ones. About 76 hours of irradiation, in 9 days, were needed with the neutron generator in 73 different poloidal and toroidal positions in order to calibrate the two neutron yield measuring systems available at JET, the 235 U fission chambers (KN1) and the inner activation system (KN2). The NG neutron emission rates provided by the monitoring detectors were in agreement within 3-4%. Neutronics calculations have been performed using MCNP code and a detailed model of JET to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the NG neutrons, and taking into account the anisotropy of the neutron generator and all the calibration circumstances. These calculations have made use of a very detailed and validated geometrical description of the neutron generator and of the neutron source routine producing neutron energy-angle distribution for the neutron emitted by the neutron generator. The KN1 calibration factor for a DT plasma has been determined with ±4.2% experimental uncertainty (1). It has been found that the difference between KN1 response to DD neutrons and that to DT neutrons is within the uncertainties in the derived responses. KN2 has been calibrated using the 93 Nb(n,2n) 92m Nb and 27 Al(n,a) 24 Na activation reactions (energy thresholds 10 MeV and 5 MeV respectively). The total uncertainty on the calibration factors is ±6% for 93 Nb(n,2n) 92m Nb and ±8% 27 Al(n,a) 24 Na (1). The calibration factors of the two independent systems KN1 and KN2 will be validated during DT operations. The experience gained and the lessons learnt are presented and discussed in particular with regard to the 14 MeV neutron calibrations in ITER.

Radiation Measurements, 1997

In this work attempts have been made to introduce a new application for CR-39 solid state nuclear track detector (SSNTD) to measure the thermal neutron flux distribution of the external neutron beam in a powder neutron diffractometer (PND) system using boric acid converter. Also a neutron radiography film with Gadolinium converter have been applied to measure the neutron flux distribution in order to compare and recheck the results obtained by the previous method.

arXiv (Cornell University), 2011

Review of Scientific Instruments, 2001

A model independent method to determine fuel ͗R͘ is to measure the energy spectrum and yield of elastically scattered primary neutrons in deuterium-tritium ͑DT͒ plasmas. As is the case for complementary methods to measure fuel ͗R͘ ͑in particular from knock-on deuterons and tritons ͓S.

Plasma and Fusion Research, 2020

Neutronics aspects of a compact D-D neutron generator as a neutron source for the neutron calibration in magnetic confinement fusion devices are assessed by the MCNP calculation. The neutron emission distribution of the compact D-D neutron generator has a large anisotropy not only due to the scattering with the neutron generator body but also due to the intrinsic anisotropy of the differential cross-section of the d(d,n) 3 He reaction. The angular neutron distribution at the target of the compact D-D neutron generator is calculated with the PHITS code where the slowing down on the accelerated deuterons in the target material is considered. The calibration experiments are simulated by using the MCNP-6 code for the ITER neutron flux monitor (NFM) to be installed in the equatorial port. The detection efficiency of NFM is calculated for a D-D plasma neutron source, an idealistic D-D neutron source, a 252 Cf neutron source and the compact neutron generator. It is found that the detection efficiency of NFM for the compact neutron generator is approximately 50% larger than that for the idealistic D-D neutron source. The discrepancy is improved to be 25% by the intention of the target 20 cm from the body of the compact neutron generator.

EPJ Web of Conferences, 2020

In this paper we propose a method of fast neutron flux estimation from a pulsed D-T neutron generator with application of single CaF2 scintillation crystal. The analysis method relies on 19 F(n, ↵) 16 N threshold activation reaction having neutron energy threshold at 1.6 MeV. As a result, the 16 N undergo β - decay with half-life of 7.1 s, emitting β particles with endpoint up to 10.4 MeV in the scintillator medium. Integration of the β distribution curve, preceded by calculation of (n, ↵) rate on F with Monte Carlo N-Particle Transport Code v6 (MCNP6) for fixed geometry, allows to estimate the neutron flux in 4⇡ per second within few minutes.

Journal of Geophysical Research: Space Physics, 2020

Review of Scientific Instruments, 2012

Characterization of single crystal chemical vapor deposition diamond detectors for neutron spectrometry Rev. Sci. Instrum. 83, 10D906 The compact neutron spectrometer at ASDEX Upgrade Rev. Sci. Instrum. 82, 123504 The new cold neutron chopper spectrometer at the Spallation Neutron Source: Design and performance Rev. Sci. Instrum. 82, 085108 Detection of high frequency intensity oscillations at RESEDA using the CASCADE detector Rev. Sci. Instrum. 82, 045101 Additional information on Rev. Sci. Instrum.

Nuclear Technology and Radiation Protection, 2013

One elec tro static ac cel er a tor based com pact neu tron gen er a tor was de vel oped. The deu te rium ions gen er ated by the ion source were ac cel er ated by one ac cel er at ing gap af ter the ex trac tion from the ion source and bom barded to a tar get. Two dif fer ent types of tar gets, the drive -in ti tanium tar get and the deuteriated ti ta nium tar get were used. The neu tron gen er a tor was op erated at the ion source dis charge po ten tial at +Ve 1 kV that gen er ates the deu te rium ion cur rent of 200 mA at the tar get while ac cel er ated through a neg a tive po ten tial of 80 kV in the vac uum at 1.3×10 -2 Pa filled with deu te rium gas. A com par a tive study for the neu tron yield with both the tar gets was car ried out. The neu tron flux mea sure ment was done by the bub ble de tec tors pur chased from Bub ble Tech nol ogy In dus tries. The num ber of bub bles formed in the de tec tor is the di rect mea sure ment of the to tal en ergy de pos ited in the de tec tor. By count ing the num ber of bub bles the to tal dose was es ti mated. With the help of the ICRP-74 neu tron flux to dose equiv a lent rate con ver sion fac tors and the solid an gle cov ered by the de tec tor, the to tal neu tron flux was cal cu lated. In this pre sen ta tion the op er a tion of the gen er a tor, neu tron de tec tion by bub ble de tec tor and es ti ma tion of neu tron flux has been dis cussed.

Plasma and Fusion Research, 2013

Fusion power output of ITER is measured by a group of neutron flux monitors combined with a neutron activation system and neutron profile monitors. These systems should be absolutely calibrated by use of DD/DT generators moving inside the ITER vacuum vessel (in-situ calibration). Each neutron monitor has a limited measurement range of emission rate, but the ranges are connected by cross-calibration using the ITER plasma with at least one decade overlapping. The over all dynamic range covered by the group of neutron flux monitors is 10 14 n/sec to 10 21 n/sec. Effects of vertical/radial movement of plasma on the measurement accuracy were reviewed. It was found that cross-calibration using specially planned jog shots, and a vertical neutron camera is important to minimize the inaccuracy caused by the plasma movement.